There's no disagreement between President Donald Trump and Secretary of State Rex Tillerson, a U.S. diplomat told CNBC.

Kurt Volker, U.S. representative for Ukraine negotiations, also said he had no reason to believe that a change in the U.S. administration is on the horizon.

"I don't think there is really a disagreement between the State Department and the White House and the Congress here. People make too much out of that," said Volker, who was appointed by Tillerson in July.

Volker's comments on Wednesday followed reports that Tillerson openly referred to Trump as a "moron" in a national security meeting and considered handing in a resignation letter in July. The two have reportedly clashed over a series of key foreign policy issues, including North Korea, Iran and Qatar.

Trump said on Twitter last Sunday: "I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man," in reference to North Korea's leader Kim Jong Un.

Volker told CNBC the president wasn't saying he was dissatisfied with Tillerson's work but simply commenting about Kim Jong Un. "I have no reason to think that there's any change coming in the U.S. administration," Volker said, referring to reports that Tillerson wanted to leave his post.

Kevin Lamarque | Reuters

President Donald Trump and Secretary of State Rex Tillerson confer during a working lunch with African leaders during the U.N. General Assembly in New York, Sept. 20, 2017.

Tillerson denied on Wednesday that he had considered leaving, and he pledged loyalty to Trump.

"There has never been a consideration in my mind to leave. I serve at the appointment of the president and I'm here as long as the president thinks I can be useful to achieving his objectives," Tillerson told reporters.